The overall goal of this research is to understand the structure-function relationships of the gonadotropins. The gonadotropins, luteinizing hormone (LH), follicle-stimulating hormone (FSH), and chorionic gonadotropin (CG), play a central role in the regulation of reproduction. Gonadotropins are used to treat infertility, to determine the time of ovulation, and to indicate pregnancy in humans. In addition, human CG is used as a tumor marker in certain cancers. Experimental models of gonadotropin action are based on action of these hormones in rats. A frequent substitute for FSH in these studies has been equine chorionic gonadotropin. The primary structure of eCG firmly establishes it as an LH/CG member of the glycoprotein hormone family, yet it is known to have FSH activity in many bioassays. Equine LH shares identical protein structure with eCG and also has FSH activity. Comparison of the activities of eCG and ELH in stimulating eCG-primed rat granulosa cells has revealed differences in their response to these hormones. Since eLH and eCG differ only in their carbohydrate moieties, this suggests that the cells are detecting these differences in carbohydrate structure. Specific aim #1 is to characterize the role of the alpha subunit oligosaccharides in stimulation of granulosa cell response. A series of hybrid hormones consisting of all possible combinations of eLH, eCG, and EFSH subunits will be prepared and their abilities to stimulate steroidogenesis in eCG- and DES-primed granulosa cells will be compared. This experiment will demonstrate whether or not differences in alpha subunit oligosaccharides are responsible for the differences in response to each hormone by these granulosa cells. The binding of eLH and eCG to frozen sections of rat ovaries will be characterized. Specific aim #2 is to investigate the role of oligosaccharides in target cell activation. Oligosaccharides purified from alpha subunits of eLH, eCG, EFSH, and pituitary free-alpha will be compared to determine the differences in populations of alpha subunit oligosaccharides on each hormone. The oligosaccharides will be tested in the granulosa cell assay systems in order to determine if they can interfere with the response to FSH stimulation.